updated 10:55 pm EDT, Mon May 12, 2014

According to reports from testers, the recently-updated beta of Safari contains within it an accelerated version of Webkit's "Nitro" JavaScript engine that could surpass current efforts in rival browsers, once fully developed. The new upgrades to Nitro, dubbed "FTLJIT," are not enabled by default in the OS X version of WebKit at present, but can be enabled through the command line, and offer substantial speed benefits.

Because JavaScript is such a crucial component of modern, media-rich web pages, its ability to dynamically reload pages, handle animated elements (such as drop-down menus) and media containers is key to the "speed" of web pages as perceived by users. One reason why Firefox is often said to "feel" faster than Safari is because developer Mozilla developed and honors some asm.js optimizations that other browsers do not. If the new FTLJIT were to adopt those optimizations, it would substantially improve instances where JavaScript is employed.

Infoworld's report on the revamped Nitro component notes that tests using the experimental FLTJIT build outperform Google's Chrome, though it is still not yet as fast as Firefox's asm.js benchmark tests. Google recently updated its own "V8" JavaScript engine. Once testing is complete, the component might be added to a future Safari build, perhaps as part of OS X 10.10 (codename "Syrah"), which Apple is working on now for release later this year. A sneak preview of 10.10 is expected at June's Worldwide Developer Conference.